用于 TRIUMF 超高剂量率 X 射线（FLASH）实验的电子-光子转换靶的设计优化。

Design optimization of an electron-to-photon conversion target for ultra-high dose rate x-ray (FLASH) experiments at TRIUMF.

作者信息

Esplen Nolan, Egoriti Luca, Paley Bill, Planche Thomas, Hoehr Cornelia, Gottberg Alexander, Bazalova-Carter Magdalena

机构信息

Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada.

Department of Chemistry, University of British Columbia, Vancouver, BC, Canada.

出版信息

Phys Med Biol. 2022 May 12;67(10). doi: 10.1088/1361-6560/ac5ed6.

DOI:10.1088/1361-6560/ac5ed6

PMID:35299167

Abstract

OBJECTIVE

To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF.

APPROACH

An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum-aluminum (Ta-Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5-1.5 mm), beam energies (= 8, 10 MeV) and electron (Gaussian) beam sizes (2σ= 2-10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress-strain conditions and fatigue life of the target assembly.

MAIN RESULTS

Dose-rates of up to 128 Gy sat the phantom surface, or 85 Gy sat 1 cm depth, were obtained for a 1 × 1 cmfield size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam (= 10 MeV, 2σ= 5 mm, = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s, albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime.

SIGNIFICANCE

Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s.

摘要

目的

在加拿大 TRIUMF 实验室的先进稀有同位素实验室（ARIEL）电子直线加速器（e - linac）上，开发一种用于小动物超高剂量率（UHDR）辐照的轫致辐射靶和兆伏（MV）级 X 射线辐照平台。

方法

用于 UHDR 放射治疗（RT）的电子 - 光子转换器设计主要围绕钽 - 铝（Ta - Al）爆炸结合靶的优化展开。分别使用 EGSnrc 和 FLUKA 蒙特卡罗（MC）代码，针对各种靶厚度（0.5 - 1.5 毫米）、束流能量（= 8、10 兆电子伏特）和电子（高斯）束尺寸（2σ = 2 - 10 毫米），评估均匀水模体和靶本身内部的能量沉积。还计算了 3D 打印小鼠模体中的深度剂量率，以推断小动物模型中用于 FLASH - RT 的 10 MV 剂量分布的兼容性。随后在 ANSYS 中进行耦合热 - 机械有限元分析（FEA）模拟，以了解靶组件的应力 - 应变条件和疲劳寿命。

主要结果

对于 1×1 平方厘米的射野尺寸、1 毫米厚的 Ta 靶以及 7.5 厘米的源皮距，使用 FLASH 模式束（= 10 兆电子伏特，2σ = 5 毫米，= 1 千瓦）时，在模体表面获得了高达 128 戈瑞/秒的剂量率，在 1 厘米深度处为 85 戈瑞/秒；此外，移除准直组件并使用更短的（3.5 厘米）源皮距可提供大于 600 戈瑞/秒的剂量率，尽管这是以射野适形性为代价的。靶温度分别保持在钽、铝和冷却水的阈值 2000℃、300℃和 100℃以下，同时铝的应变行为在各处均保持弹性，并有助于确保转换器在规定的 5 年使用寿命内正常运行。